JP2003087080A - Surface acoustic wave element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device employing an inexpensive flip chip technique, which is capable of reducing an ohmic loss by reducing an electrode resistance and operates at a high-frequency band. SOLUTION: In the surface acoustic wave device, in which a surface acoustic wave element is bonded to a package by flip-chip technique, the surface acoustic wave element 14 is provided with an IDT electrode 3, bus bar electrodes 4, 5, reflector electrodes 6, 7, routed electrode pads 8, 9, and electrode pads 10, 11 which are formed on a piezoelectric substrate 2. In this device, conductive films Xb, Xc which are defined as a first metal film are formed on the pads 10, 11, and conductive films Xb, Xc which are defined as a second metal film are also formed on at least one of the electrodes 4, 5 and the electrodes 8, 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave element, and more particularly to a surface acoustic wave element joined to a package by a metal bump and a method for manufacturing the same.

[0002]

2. Description of the Related Art With the increase in frequency of mobile communication, it is required that surface acoustic wave devices used in mobile communication can be used in a high frequency range. The surface acoustic wave device has a surface acoustic wave element using a piezoelectric substrate and a package that houses the surface acoustic wave element. Since the acoustic velocity on the surface of the piezoelectric substrate of the surface acoustic wave element is about several thousand m / sec, when the surface acoustic wave element operating at about 800 MHz is configured, the wavelength of the interdigital electrode of the surface acoustic wave element is about several μm. Becomes shorter. Therefore, there is a problem that the absolute value of the electrode film thickness for optimizing the characteristics of the surface acoustic wave element becomes small and the loss due to the electrode resistance, that is, the ohmic loss becomes large.

As a solution to the above problems,
Japanese Unexamined Patent Publication No. 7-212175 discloses that in FIG.
The surface acoustic wave device shown in (b) is disclosed. In addition,
FIG. 5B shows Q-Q between the one-dot chain line P-P in FIG.
FIG. 3 is a schematic cross-sectional view in which the end faces between the space and R-R are combined,
The dashed-dotted lines S and T in FIG. 5B indicate the boundaries of the connecting portions. In addition, in the drawings attached to this specification, FIG.
Similar to (a) and (b), in the plan view, PP
The cross sections of the portions indicated by the lines, the QQ line, and the R-R line are shown as being joined by one-dot chain lines S and T in the cross-sectional view corresponding to the plan view.

The surface acoustic wave device 20 described in this prior art.
1, the interdigital electrode 20 is formed on the piezoelectric substrate 202.
3 and reflector electrodes 204 and 205 provided on both sides of the interdigital electrode 203. Also,
Routing electrodes 206 and 207 for electrically connecting to the interdigital electrode 203 are formed. Further, electrode pads 208 and 209 are formed so as to be electrically connected to the routing electrodes 206 and 207. The electrode pads 208 and 209 correspond to the parts electrically connected to the electrodes of the package, and metal bumps are provided on the electrode pads 208 and 209. This surface acoustic wave device 2
In No. 01, among the various electrodes described above, the interdigital electrode 203, the reflector electrodes 204 and 205, and the conductive film 212 shown in FIG. 5B are formed. Also,
As shown as a representative of the electrode pads 208 and 209 in FIG. 5B, at least a part of the electrode pads 208 and 209 or the leading electrodes 206 and 207 is the second conductive film 2.
13 are stacked. That is, as compared with the interdigital electrode 203, the thickness of a part of the routing electrodes 206 and 207 and the electrode pads 208 and 209 is made thicker, thereby reducing ohmic loss due to electrode resistance and improving electrical characteristics. It is supposed to be done.

By the way, in recent years, there has been a demand for downsizing and height reduction of electronic parts, so that a surface acoustic wave device using a flip chip method has been put into practical use. In the surface acoustic wave device configured by using the flip chip method, the electrode forming portion of the surface acoustic wave element is opposed to the package mounting surface, and the electrode of the surface acoustic wave element and the electrode of the package are bonded by a metal bump. In this case, a metal film such as Au is formed on the electrode pad of the surface acoustic wave element in order to increase the bonding strength between the metal bump and the electrode pad. This Au
A metal bump made of Au or the like is formed on the metal film made of, for example, and the metal bump is bonded to the electrode surface of the package. Alternatively, there is used a method in which a metal film made of Ag or the like having excellent solder wettability is formed on an electrode pad, and a solder bump previously formed on a package is bonded to the metal film having excellent solder wettability. .

When the above method is used, no bonding wire is required. Therefore, it is not necessary to provide a wire pad to which the bonding wire is connected to the surface acoustic wave element, so that the plane area and height of the surface acoustic wave device can be reduced.

Also in the surface acoustic wave device obtained by using these flip chip construction methods, if the film thickness of the electrode other than the electrode on which the surface acoustic wave is actually excited and propagates is made thick, the ohmic loss becomes small. It is possible to suppress the loss and the reduction of the Q of the resonator. In this case, the electrodes on which surface acoustic waves are excited and propagated, that is, the interdigital and reflector electrodes, the bus bar electrodes, the lead-out electrodes, and the electrode pads are first formed of the same conductive film. next,
The second conductive film may be laminated or the thickness of the first conductive film may be increased in the electrode provided in a portion other than the portion where the surface acoustic wave is excited and propagates.

Therefore, when the bonding is performed by the metal bump, the metal film such as Au described above is laminated on the thick conductive film on the electrode pad, and then Au is formed.
Metal bumps such as the above may be formed. Further, in the case of joining with a solder bump, a metal film made of Ag or the like having excellent solder wettability is formed on an electrode pad which is formed thick by stacking a plurality of conductive films or increasing the film thickness of the conductive film. do it.

FIGS. 6 (a) and 6 (b) are a plan view and a schematic cross-sectional view for explaining a conventional method of manufacturing a surface acoustic wave device using a flip chip method which operates at a low frequency. .

In this method, the IDT electrode 2 is formed by patterning the conductive film 222 on the piezoelectric substrate 221.
23, bus bar electrodes 224, 225, reflector electrode 22
6, 227, routing electrodes 228, 229 and electrode pads 230, 231 are formed. Next, as shown in FIGS. 7A and 7B, on the electrode pads 230 and 231,
The conductive film 232 and the metal film 233 are stacked. Conductive film 2
32 is provided to enhance the adhesion with the conductive film 222, and the metal film 233 is provided to enhance the bonding strength between the metal bump 234 and the electrode pad shown in FIGS. 8A and 8B. It is being done.

Therefore, in this method, after patterning the conductive film 222, the conductive film 232 and the metal film 23 are formed.
3 had to be stacked. On the other hand, in the case of obtaining a surface acoustic wave device that operates in a high frequency range, as described above, in order to reduce the ohmic loss, as shown in FIGS. 9A and 9B, on the conductive film 232, Conductive film 222
A conductive film 241 made of the same material as that for forming the film is stacked, and the conductive film 232 and the metal film 23 are formed on the conductive film 241.
3 had to be stacked.

In addition, in the production of a surface acoustic wave device operated in a low frequency region, the surface acoustic wave device is joined to the package by a solder bump formed on the package instead of the metal bump made of Au or the like. The conductive film 222 patterned as shown in FIG.
10A and 10B, a metal film 232 for increasing the adhesion strength with the conductive film 222 and a metal film 242 serving as a solder barrier are formed on the electrode pad after the formation on the electrode pad. The metal film 243 having excellent solder wettability must be finally stacked. That is, it was necessary to form a laminated structure in which three metal layers were laminated. Also in this case, in order to reduce the ohmic loss in the surface acoustic wave device operating at a high frequency, as shown in FIGS. 11A and 11B, a conductive film 222 is formed on the metal film 232. It was necessary to stack conductive films 244 made of the same electrode material, and then form a multilayer structure made of the plurality of metal films 242 and 243.

On the other hand, in WO99 / 05788,
There is disclosed a surface acoustic wave element in which at least one of a bus bar and an electrode pad is composed of a first conductor layer containing Al as a main component / intermediate layer / a second conductor layer containing Al as a main component. Here, at least one of the bus bar and the electrode pad is configured to have the above laminated structure. Therefore, it is described that the mechanical strength is enhanced when the electrode pad has the above-mentioned laminated structure and is made thick. WO99 / 05788 describes a structure in which wire bonding or Au bumps are formed on this electrode pad.

[0014]

As described above, when manufacturing a surface acoustic wave device that operates in a high frequency region, when connecting the surface acoustic wave element and the package by metal bumps on the surface acoustic wave element, and When manufacturing a surface acoustic wave device that operates in a low frequency region in any case where the surface acoustic wave element and the package are connected by a metal film on the surface acoustic wave element and a solder bump provided on the package In comparison with the above, it was necessary to additionally stack one or more conductive films 241 and 244 in a portion other than the region where the surface acoustic wave was excited and propagated. Therefore, there is a problem that the process is complicated and the cost is high.

In the structure described in WO99 / 05788, the electrode pad has a first conductor layer containing Al as a main component /
It is composed of an intermediate layer / a second conductor layer containing Al as a main component. However, in this structure, when a solder bump is formed, since the uppermost layer of the electrode pad is composed of the second conductor layer containing Al as a main component, the solder diffuses and sufficient bonding strength can be obtained. There was a problem that I could not.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to use a surface acoustic wave element which is used in a high frequency region and which is housed in a package by a flip chip method, and simplifies the manufacturing process. It is possible to provide a surface acoustic wave element which is capable of stably obtaining good electrical characteristics by reducing ohmic loss, and which has excellent bump bonding strength when a solder bump is used, and a method for manufacturing the same. .

[0017]

A surface acoustic wave device according to the present invention is a surface acoustic wave device that is housed in a package and is joined to the package by solder bumps formed on the side of the package. At least one interdigital electrode formed on the piezoelectric substrate, a pair of busbar electrodes connected to the interdigital electrode, and a lead-out electrode connected to the busbar electrode,
An electrode pad connected to the lead-out electrode and electrically connected to the package; and a first metal film formed on the electrode pad to enhance bonding strength with the solder bump, A second metal film made of the same material as the first metal film and formed on at least one of the bus bar electrode and the lead-out electrode.

In another particular aspect of the present invention, the first,
The second metal film has a multilayer structure in which a plurality of metal layers are laminated. In this case, the uppermost metal layers of the first and second metal films are made of a metal material having excellent bonding properties to the solder bumps, and the other metal layers are made of, for example, a metal material having a low electric resistance. With the configuration, both the improvement of the bonding strength with the bump and the improvement of the ohmic loss reduction effect can be expected.

In a specific aspect of the surface acoustic wave element according to the present invention, the first and second metal films have a multilayer structure in which a plurality of metal layers are laminated, and the metal layer located at the top is , A
It is composed of g or Au. In this case, since the metal layers located on the uppermost portions of the first and second metal films have excellent solderability, the first metal film can be firmly attached to the electrode land of the package via the solder bumps. It can be easily joined.

In a more limited aspect of the present invention, the interdigital electrode has a multilayer structure in which a plurality of metal layers are laminated, and at least one metal layer of the first and second metal films comprises: Among the metal layers forming the interdigital electrode, the metal layer is made of a metal having a smaller specific resistance than that of the lowermost metal layer, whereby the ratio of at least one metal layer of the first and second metal films is increased. Since the resistance is relatively low, the ohmic loss in the metal film can be further reduced, and the thickness of the metal layer of the second metal film made of a metal having a relatively low specific resistance can be reduced.

A method of manufacturing a surface acoustic wave device according to the present invention is a method of manufacturing a surface acoustic wave device constructed according to the present invention, wherein at least one of the interdigital electrodes, a bus bar electrode, and a routing electrode are provided on a piezoelectric substrate. And a step of forming an electrode pad, and a step of forming a first metal film on the electrode pad and a second metal film on at least one of the bus bar electrode and the leading electrode.

A communication device according to the present invention is characterized by including a surface acoustic wave device constructed according to the present invention as a bandpass filter.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention.

FIGS. 1 (a) and 1 (b) are a plan view and a schematic sectional view for explaining a surface acoustic wave element according to an embodiment of the present invention, and FIGS. 2 (a) to 2 (d). FIG. 6 is a schematic cross-sectional view for explaining the method for manufacturing the surface acoustic wave element of the present embodiment.

In this embodiment, the surface acoustic wave element is joined to the package by the flip chip method by the solder bumps provided on the package. In this embodiment, FIG.
The surface acoustic wave element 54 shown in (a) and (b) is prepared. In the surface acoustic wave element 54, the rectangular plate-shaped piezoelectric substrate 42
Above the IDT electrode 43, a pair of bus bar electrodes 44, 4
5, the reflector electrodes 46 and 47, the lead-out electrodes 48 and 49, and the electrode pads 50 and 51 are formed of the conductive film Xa.

As the piezoelectric substrate 42, LiTaO ₃ , Li
Piezoelectric single crystals such as NbO ₃ or quartz, or piezoelectric ceramics such as lead zirconate titanate based ceramics may be used.

The conductive film Xa is made of a suitable conductive material such as Al. The method of forming the conductive film Xa on the piezoelectric substrate 2 is not particularly limited, and an appropriate method such as vapor deposition, sputtering or plating can be used.

Bus bar electrodes 44, 45, lead-out electrode 4
8, 49 and the electrode pads 50, 51 except for a part of the periphery of the electrode pads, the metal film Xb, the metal film Xd serving as a solder barrier layer, and the metal film X having excellent bondability with the solder bumps.
e are stacked. The metal film Xb is made of, for example, NiCr or Ti, and serves as a solder barrier layer.
It is provided to increase the adhesion strength between the conductive film Xa and the conductive film Xa. The metal film Xe is made of a metal having excellent bondability with the solder bump, for example, Ag. In addition, the metal film Xd that serves as a solder barrier layer is made of an appropriate metal such as Ni, which is unlikely to cause solder erosion.

In this embodiment, the IDT electrode 4
Although 3 is formed, a plurality of IDT electrodes may be formed and the reflector may not be formed. In order to obtain the surface acoustic wave element of this embodiment, a conductive film Xa is formed on the entire surface of the piezoelectric substrate 42, and then patterned to form a conductive film Xa.
The patterned conductive film Xa is formed on the piezoelectric substrate 42.

That is, as shown in FIG. 2A, a patterned conductive film Xa is formed on the piezoelectric substrate 42.
Is formed. Thereby, the IDT electrode 43, the reflector electrodes 46 and 47, the bus bar electrodes 44 and 45, the leading electrodes 48 and 49, and the electrode pads 50 and 51 are formed by the conductive film Xa.

Thereafter, as shown in FIG. 2A, a resist 61 is laminated on the entire surface. Next, the resist of the unnecessary portion is removed by exposure and development using a photomask, and the resist 61 is patterned.

Thus, as shown in FIG. 2 (b),
A patterned resist 61A is formed. In this state, the IDT electrode 43 and the reflector electrodes 46, 4
7 and a part of the electrode pads 50 and 51 are covered with the resist 63A.

Then, as shown in FIG. 2 (c), Ni
A metal film Xb made of Cr or Ti is formed.
Next, N which functions as a solder barrier layer is formed on the metal film Xb.
A metal film Xd made of i or the like and a metal film Xe made of Ag or the like having excellent wettability to solder are sequentially formed on the entire surface. The formation of these metal films Xb, Xd, and Xe can be performed by an appropriate method such as vapor deposition and sputtering.

Thereafter, the conductive film X on the resist 61A is formed.
b, Xd, and Xe are lifted off together with the resist 61A. In this way, as shown in FIG. 2D, the bus bar electrodes 44 and 45 and the routing electrodes 48 and 49 are formed.
And the metal films Xb, X on the electrode pads 50, 51.
Laminated metal films made of d and Xe are laminated to obtain the surface acoustic wave element 54 shown in FIG.

When the surface acoustic wave element 54 is bonded to the package, as shown in FIG.
Solder bumps 12, 13 provided on the electrodes 14, 15 of the
So that the electrode pads 50, 51 are in contact with each other.
It is mounted on Nos. 4 and 15. Then, the surface acoustic wave element 54 is bonded to the electrodes 14 and 15 of the package 11 through the solder bumps 12 and 13 by heating, and the surface acoustic wave device of this embodiment is obtained.

In this embodiment, the metal films Xb, Xd, Xe are formed on the bus bar electrodes, the lead-out electrodes and the electrode pads.
Are stacked. Metal films Xb, Xd on the electrode pad,
Xe forms the first metal film of the present invention, and the metal films Xb, Xd, and Xe on the bus bar electrode and the leading electrode form the second metal film. Therefore, in these electrode parts,
Similar to the structure in which a conductive film made of the same electrode material as the conductive film Xa is laminated on the conductive film Xa, the electrode resistance can be reduced and the ohmic loss can be reduced. Therefore, as in the first embodiment, the elasticity of the conductive film Xa can be reduced without using the step of stacking conductive films made of the same electrode material as the conductive film Xa to reduce ohmic loss, that is, without complicating the electrode forming step. The loss of the surface acoustic wave device and the decrease of Q can be suppressed.

In this embodiment, the thickness of the metal film Xe for joining with the solder bump is not necessarily the same as that of the IDT electrode 4.
It is not necessary to make it thicker than the thickness of the conductive film Xa that forms No. 3. That is, the specific resistance of the metal films Xb to Xe is equal to that of the conductive film X.
If it is smaller than the specific resistance of a, the metal films Xb, Xd, Xe
Need not be thicker than the thickness of the conductive film Xa.

FIG. 3 shows the impedance-frequency characteristics of the surface acoustic wave device constructed according to this embodiment by a broken line. For comparison, the solid line shows the characteristics of the comparative example in which the bus bar electrode and the lead-out electrode are not thickened, and the electrical characteristics of the conventional example in which the conductive film portion made of the same electrode material as the IDT electrode is thickened according to the conventional method. Is indicated by a chain line. As is clear from FIG. 9, in this example, a resonance characteristic with a large Q is obtained as compared with the comparative example in which the bus bar electrode is not thickened, and the resonance characteristic equal to or higher than that of the conventional example is obtained. I understand.

In the present embodiment, the second metal film is formed on the bus bar electrode and the leading electrode, but the second metal film is provided to reduce ohmic loss, and the bus bar electrode and the leading electrode are arranged. It may be laminated only on one of the electrodes, or may be partially formed on a part of the bus bar electrode and the leading electrode.
However, it is preferable that the second metal film is laminated on both the bus bar electrode and the leading electrode, as described in the present embodiment.

[0040]

In the surface acoustic wave device and the method of manufacturing the same according to the present invention, the surface acoustic wave device is made of the same material as the first metal film formed on the electrode pad for increasing the bonding strength with the solder bump on the package side. The second metal film is formed on at least one of the bus bar electrode and the leading electrode.
That is, the first electrode formed on the electrode pad for the purpose of increasing the bonding strength with the solder bump on the package side.
In the metal film forming step, the second metal film made of the same material is formed on at least one of the bus bar electrode and the leading electrode. Therefore, the resistance loss of the electrode can be reduced without complicating the manufacturing process. Therefore, it is not necessary to increase the film thickness of the bus bar electrode and the lead-out electrode in a separate step, and thus the manufacturing cost of the surface acoustic wave device formed by the flip chip method can be reduced.

In addition, since the bus bar electrode and the lead-out electrode are made thicker by the metal material having the excellent adhesion strength to the conductive film forming the IDT electrode, the bus bar electrode and the lead-out electrode can be formed as the IDT electrode. It is possible to obtain characteristics equal to or higher than those obtained when a thick film is formed by using the same electrode material.

[Brief description of drawings]

1A and 1B are schematic plan views for explaining a surface acoustic wave element according to an embodiment of the present invention, and a PP line, a QQ line, and an R- line in FIG. The typical sectional view which joined the portion which followed the R line via the dashed-dotted line S and T.

2A to 2D are schematic cross-sectional views for explaining the electrode structure of the surface acoustic wave element of the embodiment.

FIG. 3 is a diagram showing impedance frequency characteristics of a surface acoustic wave element of an example, a surface acoustic wave device prepared for comparison, and a surface acoustic wave element configured according to a conventional method.

FIG. 4 is a schematic sectional view for explaining a surface acoustic wave device according to an embodiment.

5 (a) and 5 (b) are schematic plan views for explaining an example of a conventional surface acoustic wave device and PP of FIG.
The portions along the line, the QQ line and the RR line are indicated by alternate long and short dash lines S, T
FIG.

6 (a) and 6 (b) are schematic plan views for explaining a process of obtaining the conventional surface acoustic wave device shown in FIG. 5, and a line PP and a line QQ in FIG. And a cross-sectional view in which the portions along the line RR are connected via the alternate long and short dash lines S and T.

7 (a) and 7 (b) are schematic plan views for explaining an example of a conventional surface acoustic wave device used in a high frequency range, and PP line and QQ line in FIG. 7 (a). And a cross-sectional view in which the portions along the line RR are connected via the alternate long and short dash lines S and T.

FIG. 8A is a schematic plan view for explaining still another example of the conventional surface acoustic wave device and PP of FIG.
The portions along the line, the QQ line and the RR line are indicated by alternate long and short dash lines S, T
FIG.

FIG. 9A is a schematic plan view for explaining still another example of the conventional surface acoustic wave device used in a high frequency range, and the PP line, the QQ line, and the PP line in FIG. Sectional drawing which joined the part along RR line through dashed-dotted line S, T.

FIG. 10A is a schematic plan view for explaining still another example of the conventional surface acoustic wave device and PP of FIG.
The portions along the line, the QQ line and the RR line are indicated by alternate long and short dash lines S, T
FIG.

FIG. 11A is a schematic plan view for explaining still another example of the conventional surface acoustic wave device, and PP of FIG.
The portions along the line, the QQ line and the RR line are indicated by alternate long and short dash lines S, T
FIG.

[Explanation of symbols]

1. Surface acoustic wave device 2 ... Piezoelectric substrate 3 ... IDT electrode 4, 5 ... Busbar electrodes 6, 7 ... Reflector electrodes 8, 9 ... Routing electrodes 10, 11 ... Electrode pad 12, 13 ... Metal bump 14 ... Surface acoustic wave element 15 ... Package 41 ... Surface acoustic wave device 42 ... Piezoelectric substrate 43 ... IDT electrode 44, 45 ... Bus bar electrodes 46, 47 ... Reflector electrode 48, 49 ... Routing electrodes 50, 51 ... Electrode pad 54 ... Surface acoustic wave element Xa ... Conductive film Xb ... Conductive film (first and second metal films) Xc ... Conductive film (first and second metal films) Xd ... Conductive film Xe ... conductive film

Continued front page    F term (reference) 5F044 QQ02 QQ04 QQ06 RR18                 5J097 AA01 AA24 AA32 BB17 DD24                       DD29 FF03 GG03 GG04 HA02                       JJ09 KK01 KK09 KK10                 5J108 AA07 BB08 CC04 EE03 EE07                       EE13 FF11 FF13 GG03 KK03

Claims (6)

[Claims] 1. A surface acoustic wave device housed in a package and joined to the package by a solder bump formed on the package side, wherein the piezoelectric substrate and at least one interdigital device formed on the piezoelectric substrate. An electrode, a pair of bus bar electrodes connected to the interdigital electrode, a lead-out electrode connected to the bus bar electrode, and an electrode pad electrically connected to the lead-out electrode and electrically connected to the package A first metal film formed on the electrode pad to enhance the bonding strength with the solder bump, and made of the same material as the first metal film, on at least one of the bus bar electrode and the leading electrode. And a second metal film formed on the surface acoustic wave element. 2. The surface acoustic wave device according to claim 1, wherein the first metal film and the second metal film have a multilayer structure in which a plurality of metal layers are laminated. 3. The first and second metal films have a multi-layer structure in which a plurality of metal layers are laminated, and the uppermost metal layer is made of Ag or Au. 1
Alternatively, the surface acoustic wave device according to item 2. 4. The interdigital electrode has a multi-layer structure in which a plurality of metal layers are laminated, and at least one metal layer of the first and second metal films constitutes the interdigital electrode. The surface acoustic wave device according to claim 2, wherein the surface acoustic wave device is made of a metal having a smaller specific resistance than the lowermost metal layer among the existing metal layers. 5. The method of manufacturing a surface acoustic wave device according to claim 1, wherein at least one of the interdigital electrode, the bus bar electrode, the lead-out electrode, and the electrode pad is formed on a piezoelectric substrate. A method of manufacturing a surface acoustic wave device, comprising: a step; and a step of forming a first metal film on the electrode pad and a step of forming the second metal film on at least one of the bus bar electrode and the lead-out electrode. 6. A communication device, comprising the surface acoustic wave device according to claim 1 as a bandpass filter.